Rotary lawn mowers, having a blade rotated in a generally horizontal plane, about a central, generally vertical rotatable shaft, are known. The blade of such a lawn mower is a generally flat elongated piece of steel which is rotationally symmetric with the rotatable shaft. The blade has a sharpened edge on the leading edge of the outer portion of the blade. The outer portion trailing edge is generally slightly raised to cause a fan effect so as to lift the grass and to blow the clippings into a bag.
The cutting edge of the mower blade becomes dull very quickly. While the mower blade appears to be cutting for a long period of time, in actuality, the cutting edge may have ceased to be a true cutting edge and may thus sever blades of grass only because the mower blade is rotating very fast. Thus, the blades of grass are broken by the spinning mower blade and are bruised in the process. The grass develops a brown tip because of the bruising, has an unpleasing appearance, and is a damaged plant. Furthermore, since the dull mower blade must break the grass blades, instead of cutting them, the motor which rotates the blade is under an increased load, thus requiring more maintenance and consuming more fuel.
In the past, the sharpening of a mower blade required the removal of the entire blade. Once the blade was removed, a new edge could be grinded or filed onto the blade. The blade would then have to be remounted onto the shaft. This procedure is very difficult and very time consuming.
Various types of replaceable cutters have been proposed to avoid the resharpening and eventual loss of the rotary blade. Such replaceable blades have presented problems of one type or another with regard to the requirement of complex fabrications, strength of the replaceable cutter, weakened resistant to damage by foreign objects, costs, and the like. There has remained a need for a blade with a strong cutter which can be easily replaced at a reasonable cost.
In the past, various U.S. patents have issued relating to replaceable cutting blades for lawn mower blades. For example, U.S. Pat. No. 3,665,692, issued on May 30, 1972, to B. F. Hughes describes a rotary mower holder with expendable blades. A bar is mounted on the shaft of the driving motor of the mower. Each of the ends of the bar define blade receiving channels at opposite ends of the bar. The expendable blades have backs which removably engage the channels. The blades are held in place by frictional engagement and centrifugal force of the blade. Retaining screws can be provided.
U.S. Pat. No. 4,229,933, issued on Oct. 28, 1980, to R. A. Bernard shows a separable mower blade having a slot disposed on the mower blade for reception of a bolt. The bolt is affixed to a stem portion affixed to the drive axis of the motor shaft and to the blade. The blade and the stem are constructed so as to allow easy removal of the blades.
U.S. Pat. No. 4,375,148, issued on March 1, 1983, to Carl E. Beck, teaches a mower blade having cutting elements which are removably attached to a base member. A removable element is held in the base member by means of a wedged slot which cooperates with a wedged part of the shank of the removable cutting element.
U.S. Pat. No. 4,611,460, issued on Sep. 16, 1986, to J. D. Parker provides a support blade with a replaceable cutter for a lawn mower. The support blade has a recess at a top portion adjacent each end which receives a replaceable cutter element. The cutter has a bottom portion which fits snugly in the recess and a laterally extending cutter element which has a front knife edge for cutting and a rear portion which abuts against the blade support in such a fashion that thrust of the cutter is distributed against the back blade support and the back of the recess.
U.S. Pat. No. 4,651,510, issued on Mar. 24, 1987, to W. J. Malutich teaches a lawn mower blade that has cutting edges on removable cartridges. The removable cartridges are affixed directly to the forward edge of the cutting blade. Threaded members are used so as to secure the removable cartridges into slots formed on the forward edge of the cutting blade.
U.S. Pat. No. 4,750,320, issued on Jun. 14, 1988, to T. J. Liebl shows a lawn mower blade having removable cutting tips snappily mounted on a blade base member. The blade can be provided with a new cutting edge by replacing the worn cutting tips with new tips without the need for removing the entire blade from the lawn mower drive spindle.
U.S. Pat. No. b 4,779,407, issued on Oct. 25, 1988, to J. G. Pattee shows a rotary lawn mower bar with non-metallic replaceable cutting and sweeping components. The rotary bar has L-shaped retaining arms, each of which passes through a central channel in a replaceable component.
U.S. Pat. No. 5,018,347, issued on May 28, 1991, to M. A. Feilen, describes replaceable cutting edges for a lawn mower blade. The blade body includes a forwardly extending flange and a rearwardly extending flange. Each flange includes a slot extending along the flange spaced from an end edge surface of the cutting blade by a predetermined distance. A polymeric replacement blade, having a T-shaped projection directed rearwardly of the blade, is receivable within the slot. The blade includes a top and bottom surface aligned with a respective top and bottom surface of the associated blade body.
U.S. Pat. No. 5,036,654, issued on Aug. 6, 1991, to W. J. Malutich describes a replaceable cutting blade for a rotary lawn mower in which the replaceable cutters are held in place by a positive locking arrangement. This locking arrangement includes a safety lock that is manually released by the user. During the operation of the mower, the centrifugal force of the rotating blade locks the cutters in place. Each of the replaceable blades includes an air-deflecting vane.
It is an object of the present invention to provide a replaceable cutting blade that is cost effective, convenient, and easy to use.
It is another object of the present invention to provide a replaceable cutting blade for a lawn mower that is easy to assemble.
It is another object of the present invention to provide a replaceable cutting blade that improves the quality of grass cutting.
It is still a further object of the present invention to provide a replaceable cutting blade that minimizes maintenance requirement, maximizes convenience, and reduces sharpening requirements.
It is still a further object of the present invention to provide a replaceable mower blade that can extend an adjustable distance from the forward edge of the mower blade.
It is still another object of the present invention to provide a replaceable mower blade that is easy to manufacture, easy to use, and relatively inexpensive.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.